Solar water heater

ABSTRACT

The invention provides an affordable solar water heater of a simple construction and a process enabling its mass production. The heater is characterized by the tank and the collector being integrated in one structurally uniform unit made of hard plastic, the unit obtained by welding two identical injected subunits.

FIELD OF THE INVENTION

The present invention relates to a solar water heater and a process for manufacturing it. The process, providing a heater at much more affordable price than other methods, is particularly suitable for mass production in developing countries. The heater is characterized by the tank and the collector being integrated in one unit, made of hard plastic. The unit is obtained by welding two, preferably identical, injected subunits.

BACKGROUND OF THE INVENTION

In search for renewable sources of energy, the use of solar energy is a foremost candidate for supplying clean power, particularly in Southern countries. Converting the sun radiation to electricity has been a successful field of the high tech research for years, increasing the efficiency of the techniques up to very practical levels. Photovoltaic cells or concentrated solar power units, whose collector- or mirror-fields give the landscape a sci-fi appearance, already supply tens of megawatts to the grid. However, simple solar water heaters, “low tech” relatives of the above techniques, still supply ten times more energy to the small users, and their importance only increases. Solar water heaters might supply hot water to millions autonomous users far from communications and industrial infrastructure, with minimal requirements for maintenance. This is particularly important for developing countries, fighting for improving hygienic conditions of their populations, while incidentally located at areas of good insolation throughout the year. An energy input of minimally 1000 kWh per year, possibly provided by a collector of about one square meter, might be a useful contribution for a family having a yearly income of $1000 or less.

A typical solar water heater (SWH) includes a flat collector and a tank for storing heated water. The collector comprises a thin snaking tube covering a plane oriented toward the sun through which water to be heated moves, circulating between the collector and the tank. Water circulates either forcibly by a pump, or passively by the convection caused by rising hot water and sinking cold water, which phenomenon is also called thermosiphon flow. Heat losses are minimized by covering the collector with a glass pane and other surfaces by an insulation layer. The SWH may be incorporated within sophisticated systems and may, for example, comprise auxiliary electrical heating, anti-freeze protection, pressure regulation, special insulation, pumps, thermostats, controllers, microprocessors, and other accessories optimizing the utilization of the sun light and enabling to employ the sun energy even under less favorable conditions of Northern but richer countries. However, even relatively simple systems comprise many components whose manufacture and assembly is complex and expensive, requiring substantial investments when installing the SWH system. It is therefore an object of the invention to provide a generally usable, inexpensive sun water heater.

Beside the cost considerations, still more frequently it is the environment concern that nowadays affect the decision making processes on all levels. Taken into account are energy demands, complexities of the components to be assembled, the use of non-recyclable materials, limiting the needs of metals, facilitated transport, and payback periods of investments. It is therefore a further object of the invention to provide a sun water heater with a simple construction, less demanding on expensive components and materials, and minimizing the use of metals. The available systems usually comprise separate components which must be transported to the site of the heater usage, assembled, and connected to the water and electrical grids by an expert, whereas the components are quite heavy and also vulnerable. There is a strong need for lighter and mechanically resistant solar heaters to withstand the transport outside good roads and to be used even at locations not connected to water and electric grids. It is therefore a still further object of the invention to provide a robust sun water heater, to be relatively light and transportable without particular precautions, which can be assembled without special training, and which can work even without being connected to electric or water lines.

In order to simplify the construction of the SWH, the tank and the collector have been suggested to be combined in more compact units, while also incorporating plastic materials. U.S. Pat. No. 4,452,231 relates to a solar heating apparatus in which the collector and tank are integrated in one container unit. The apparatus is formed by a stacked array of vertical tubular tanks, each tank provided with a heat conducting plate and a pipe, and an opening with a pressure valve. The apparatus combines insulating plastics with well conducting metals. U.S. Pat. No. 4,499,894 relates to a solar water heater, integrating the collector and the tank in one plastic container; the complex structure comprises several polymer layers of various thicknesses, and a metal coil heat exchanger. U.S. Pat. No. 5,462,047 relates to a solar water heater with a collector integrated with storage tank, provided with a plurality of flow valves and thermostatic sensors. WO 01/67008 describes a solar water heater made of plastic materials, comprising a flat collector and a barrel-like tank integrated in a housing, the tank being connected to the collector with a pipe. WO 86/03280 relates to a solar water heater comprising a flat collector and a barrel like tank integrated in a single unit made of plastic. WO 2009/125384 relates to a water tank with integrated solar collector, the upper face of the tank having ridges and acting as said collector; the material of the whole device may be selected from metal, glass, or plastic. The existing sun water heaters have features which preclude their mass production and their use as inexpensive robust devices. The heaters employ complex components and expensive materials, and would not be easily transported and assembled. Some of the devices comprise complicated compartmentalization of the internal volumes, others would not be enough stable during the real work situations. It is therefore another object of the invention to provide a process for manufacturing sun water heaters enabling a mass production of simple and stable devices, affordable also in developing countries.

It is also an object of the invention to provide an inexpensive sun water heater mechanically resistant to transport in the field conditions, and easy to assemble by untrained users.

Other objects and advantages of present invention will appear as description proceeds.

SUMMARY OF THE INVENTION

This invention provides a solar water heater comprising a container for holding water of a volume between 60 and 200 liter, and a sun light collector of a surface between 0.8 and 2 m², integrated in one body essentially having a parallelepiped shape, the body comprising two connected half units, each unit injection molded from a thermoplastic polymer. Useful are polymers like polypropylene, polycarbonate, or ABS, but other polymers suitable for containing hot water and for undergoing welding or bonding may be employed. In an important embodiment of the invention, a solar water heater is provided which comprises two half-units being heat welded. In one embodiment of the invention, said half-units are identical. The heater has usually the shape of a flat parallelepiped made of two plastic, injection molded, half units, comprising rectangular upper and bottom faces, and a transparent sheet mounted on said upper face and a non-transparent plastic sheet mounted on said bottom face. In a preferred embodiment of the invention, said body of the heater comprises an upper face and a bottom face of the same rectangular shape, and columns protruding from said upper face downward and columns of the same shape protruding from the bottom face upwards, the two column systems being positioned against each other, each column touching a column from the opposite wall, the double column height essentially determining the distance of said two faces, the columns in each pair of the opposite columns being tightly connected by heat welding. The solar water heater according to the invention comprises essentially no partition means for separating water absorbing the sun light from water stored for later use.

The invention relates to a solar water heater consisting essentially of three main structural components: one compact body, a transparent sheet, and a non-transparent sheet, the heater being made of plastic, except for said transparent sheet which may be made of glass. Said compact body has an upper face and a bottom face and is obtained by heat welding of two identical half-units prefabricated by injection molding, said transparent sheet mounted onto said upper face and said non-transparent sheet under said bottom face.

The invention provides a method for manufacturing a solar water heater comprising a container for holding water and a sun light collector of a rectangular surface integrated in one body essentially exhibiting a parallelepiped shape, comprising i) mold injecting a half-unit having essentially the shape of a an open flat parallelepiped having one base and lateral faces (side walls), the base and faces defining a half of the internal volume of said heater, and columns protruding from said base within the internal volume having a height approximately equal to the height of said side walls; ii) precisely apposing two half-units injected according to step i) in such a way that each column from one half-unit touches or nearly touches a columns from the second half-unit; iii) joining said two half-units, thereby closing said internal volume in a water-proof manner, the volume serving as a tank for containing water to be heated; and iv) mounting a transparent sheet onto one base of said tank, and a non-transparent sheet onto the other base of said tank. Said two half units are preferably joined by heat welding. In a preferred embodiment of the method according to the invention, said two half units are identical. In one embodiment of the invention, the solar water heater comprises a plastic body formed by welding two identical half-units, each formed by injection molding, said body having an upper face, a bottom face, and lateral faces, said upper face being depressed, and said bottom face being elevated, said upper face enclosing an upper insulating air layer together with the lateral faces and with said transparent sheet, and said bottom face enclosing a bottom insulating air layer together with the lateral faces and with said non-transparent sheet. When relating to the depressed and elevated positions of the faces, what is meant is that the upper and bottom walls are positioned somewhat nearer to the center of the parallelepiped-like heater body than ideal parallelepiped bases, being moved toward each other in the direction perpendicular to the plane of the faces (bases), making place for the two insulating air layers and for two sheets closing the insulating spaces. Said injection molded half-units comprise structural features enabling to functionally close the internal volume of the water tank, to mount the transparent and non-transparent sheets on the tank, and to connect the heater with pipes and desired accessories. Said injection molded half-units are preferably shaped to provide maximal mechanical strength at minimal weight.

The invention provides a solar water heater and a manufacturing process for making same, wherein the main structural component of said heater consists merely of one compact polymer body, obtained by heat welding, or by bonding, of two identical half-units prefabricated by injection molding of a thermoplastic polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other characteristics and advantages of the invention will be more readily apparent through the following examples, and with reference to the appended drawings, wherein:

FIG. 1. shows a perspective schematic view of a solar water heater adjusted in a position facing the sun, in one embodiment according to the invention;

FIG. 2. shows a schematic cross sectional view of a heater like that one shown In FIG. 1, along the line A-A′, with respect to the circulation of water in the tank being heated by the sun rays, the arrows roughly perpendicular to the collector surface represent sun rays, and the arrows inside the heater show the water circulation due to thermo_siphon flow;

FIG. 3. is a cross section of a heater similar to one shown in FIG. 1 along the line A-A′, schematically showing assembling two identical injected plastic parts (1) and (2), and two sheets (5) and (6) ensuring insulation; parts (1) and (2) are apposed and heat-welded along plane (3), parallel to sheets (5) and (6);

FIG. 4. is a scheme of a cross section of a heater similar to one in FIG. 1 along the line A-A′, showing elements protruding from two outer surfaces inward to the tank in an alternative configuration than in FIG. 3;

FIG. 5. shows a perspective schematic view of a solar water heater in accordance with one embodiment of the invention, comprising several optional features; and

FIG. 6. shows a perspective schematic view of series of solar water heaters according to one embodiment of the invention, aiming at increasing the device capacity.

DETAILED DESCRIPTION OF THE INVENTION

Solar water heaters usually consist of a collector unit and a spatially separated container unit for storing the heated water, the former unit comprising coiled tubing arranged in the heat-absorbing plane, the latter unit being often a cylindrical tank, wherein the two units are connected with pipes in which water is circulated either by convection (passive system) or by pumping (active system). Some heaters integrate the two units in more compact arrangement, but often keeping typical features of the above described dual construction, such as tubing coil and/or separation of the spaces in which the water is heated and stored, frequently comprising complex compartmentalization designs. A much simpler structure has now been provided by the invention, fully eliminating the shape differentiation between the collecting and storing parts, and entirely abandoning the spatial division between the collector and the tank; the structural materials comprise thermoplastic polymers, wherein the main body of the heater preferably consists of two identical parts welded together, each part being injection molded into a shape ensuring maximal mechanical strength at minimal weight of the solar heater. In view of the simplicity of the product and the process for manufacturing it, the structurally uniform solar water heater of the invention provides a surprisingly good performance.

In a preferred embodiment of the invention, the main structural component of the sun water heater of the invention consists merely of one compact polymer body, obtained by heat welding or by bonding of two identical half-units prefabricated by injection molding of a thermoplastic polymer. Said half-units may be easily and cheaply manufactured by injection molding routinely employed in mass production of polymer parts. Said body may have essentially the shape of a flat rectangular parallelepiped, whose top and bottom bases are depressed in the direction toward each other, reducing the inner volume of the tank. The edges of upper and bottom faces (two bases) serve for mounting sheets of essentially the same shape as the two bases: a transparent sheet is mounted above the top base, and a non-transparent sheet is mounted below the bottom base. Said transparent sheet may be a glass pane or transparent plastic, said non-transparent sheet is plastic. Said top base of said body, together with the lateral faces and with the transparent sheet enclose a space which serves to create greenhouse effect and to reduce the heat loss from the illuminated base. Said bottom base of said body, together with the lateral faces and with the non-transparent sheet enclose a space which serves to reduce the heat loss from the non-illuminated base, by creating an insulating layer of air. The lateral bases serve for attaching adjustable legs or other means for positioning the body in the required position, for example on a flat roof, or on slanted roof, or on other elevated structure. Said lateral faces also comprise a hole for connecting an inlet tube bringing cold water in and a hole for connecting an outlet tube for taking hot water out; the former hole being positioned as low as possible, and the latter hole as high as possible.

In one embodiment, the solar water heater according to the invention may have a general appearance as schematically depicted in FIG. 1. The flat rectangular parallelepiped has an internal volume of, for example, about 100 liters, serving as a tank for storing water to be heated. The body of the heater was obtained from the injected upper half (1) and injected lower half (2), by hot welding along the plane (3), thereby closing said internal volume. The outer surface of the upper wall (17) absorbs the heat from the sun radiation and transfers it to the heated water. In parallel to said outer surface, a transparent sheet (seen as (5) in FIG. 3), preferably glass pane, is mounted at the edges (4), positioned above said upper wall and closing a layer of air between said wall, said sheet, and lateral faces of said parallelepiped. The layer insulates the water in the tank, and the transparent layer reduces, due to greenhouse effect, the heat escape. The bottom wall, parallel to said upper wall but being a part of said lower half (2) forms the base of said tank. In parallel to said bottom wall, mounted to edges 4′, is a plastic sheet positioned below said bottom wall and closing a layer of air between said wall, said sheet, and lateral faces of said parallelepiped; the layer insulates the hot water in the tank. Associated with the edges 4 and 4′ are the means for fixing said insulating two sheets in position. Said means may comprise, for example, slots shaped in the internal side of the lateral faces and having a width for inserting the sheet, forming rails for sliding the sheets into the position. Columns (7), protruding from the upper wall, are part of said injected upper half and serve for bolstering the transparent sheet, and optionally for fixing it in position such as by gluing; similar columns stick out of the bottom wall, bolstering the plastic sheet. The upper wall (17) and the lateral faces comprising the edges (4) are integrated in said injected upper half (1), similarly as the bottom wall and the lateral faces comprising edges (4′) are integrated in the injected lower half (2). Said upper wall and said lateral faces are parts of said injected upper half, the reinforcement ribs (8) being a part of the connection between the upper wall and the side walls (lateral faces) (see also FIG. 3). This rib is vertical to plane 17. The arrows 11 shows the direction of cold water entering the heater through an inlet pipe connected through the lateral face of said heater, the inlet hole in the heater body preferably being provided by a screw thread for attaching a complementary inlet pipe. The arrows 12 shows the direction of hot water leaving the heater through an outlet pipe connected through the lateral face of said heater, the outlet hole (12′) for inserting the pipe being prepared in the same way as said inlet hole. Water circulation in the plain of the cross section A-A′ is shown in FIG. 2; ascending hot water and descending cold water cause convection, similarly as in thermosiphon flow used in classical passive systems, but in the current device the heat is transferred not between a tank and a collector but between two flat adjacent sections of said parallelepiped (the layers touching the upper and the bottom walls), and the flow does not comprise a cylindrical stream through a tube but a thin layer stream inside the continuous, essentially undivided space of the parallelepiped tank.

In an important aspect of the invention, the main part of the solar water heater is a compact rectangular plastic block obtained by connecting two, preferably identical, parts. Said parts are injection molded, and include all important construction features of the heater already incorporated in the mold. In one embodiment, two slightly different half-units are injection molded and connected. The connection may include mechanical means, or gluing, or heat welding. In a preferred embodiment, two identical injected units are heat welded. Two identical units having mirror symmetry are provided, one of them is rotated (by 180° around an axis parallel with the outer absorbing wall) and apposed to the other unit, thereby enclosing the volume for containing water. The parts of the two units which touch each other are preferably heated and welded. FIG. 3 shows an arrangement of the two units touching each other before welding, according to one embodiment the invention. The injected upper half (1) is preferably identical with injected lower half (2), shown appended before hot welding along the plane (3); welding closes the internal, essentially undivided, volume (10) which serves for containing water to be heated. The outer surface of the upper wall (17) absorbs the heat from the sun radiation and transfers it to the heated water. In parallel to said outer surface, the transparent sheet (5), preferably glass pane, is mounted at the edges (4), the sheet positioned above said upper wall (17) and closing a layer of air (18) between said wall (17), said sheet (5), and lateral faces of said parallelepiped (24). The bottom wall (17′), parallel to said upper wall but being a part of said lower half (2) forms the base of said tank. In parallel to said bottom wall, mounted to edges 4′, is a plastic sheet (6) positioned below said bottom wall (17′) and closing a layer of air (19) between said wall (17′), said sheet (6), and lateral faces of said parallelepiped (24′); the layer insulates the water in the tank. Associated with the edges 4 and 4′ are the means for fixing said insulating two sheets in position; the means may comprise mechanical arrangement to fix the sheets in the position, possibly associated with the edges 4 and 4′, and columns 7 and 7′; the means may comprise gluing. Columns (7), protruding from the upper wall, are part of said injected upper half and serve for bolstering the transparent sheet, and optionally for fixing it in position; similar columns (7′) stick out from the bottom wall, bolstering the plastic sheet. The upper wall (17) and the lateral faces (24) comprising edges (4) are integrated in said injected upper half (1), similarly as the bottom wall (17′) and the lateral faces (24′) comprising edges (4′) are integrated in the injected lower half (2). Said upper wall and said lateral faces are shaped within the continuous plastic block (1), the structure being further reinforced by the ribs (8); similarly, ribs (8′) reinforce continuous plastic block (2). Columns 9 extend from the internal surface of the upper wall (17) toward the bottom wall (17′), and columns 9′ extend from the internal surface of the bottom (17′) toward the upper wall (17). During the process of heat welding, the columns 9 and columns 9′ are joined; also joined, along the plane (3), are parts of lateral faces 24 of the upper half (1) with parts of the lateral faces 24′ of the lower half (2). The columns 9 and 9′ reinforce the whole body of the solar heater according to the invention, without compartmentalizing the inner volume of the heater, which volume remains undivided. The outer walls of the main plastic body may be, for example, 5-10 mm thick. The outer surface of the upper wall before covering with said transparent sheet may be corrugated or roughened to improve the heat absorption.

In one embodiment, the solar water heater of the invention may comprise two half-units which are connected during the manufacturing process to form the body for containing water to be heated, wherein said half-units are different. In one embodiment of the invention, the columns extending from one of the half-units are of a male type and the columns extending from the other half-unit are female type, wherein the male columns are inserted to the female, hollow columns, during joining the two halves, as schematically shown in FIG. 4. The surfaces of the two types of columns, which are in contact, may be adjusted to stabilize the connection, possibly comprising glue or mechanical means, like roughening the surface or employing return hooks, and the like.

In another embodiment of the invention, the solar heater may be provided by various accessories. FIG. 5 schematically shows a solar water heater in accordance with one embodiment of the invention. Insulation material (22) is comprised along the side walls and the bottom wall of the tank. A transparent sheet (5) covers the exposed surface of the tank. Braces (9) extend inwardly through the upper wall, through the inside of the tank and out through the lower wall of the tank. The braces, in one embodiment, are formed by two parts, pressed to fit together so that their respective complementary male (9 a) and female (9 b) parts engage when an upper and lower molded half-units are attached. In one embodiment, the upper and lower moldings are molded so that each major opposing side (the upper and lower walls) have circumferential inwardly extending flanges. The edges of the flanges are joined to form the tank for heated water. The unit includes an inlet (11) at a lower end thereof, and an outlet (12) at an upper end thereof to allow cold water to be added to the tank at its operatively lower end and hot water to exit at its operatively upper end. An electrical water heater element (27) may extend into the tank through a side wall thereof. The heater element may be connected to an electrical control circuit (23) which, in turn, is connected to mains electricity supply (20). A pressure release valve (21) is attached in the upper wall, or in the side wall, to allow for pressure release form the tank at a predetermined pressure.

In one aspect of the invention, several water heater units are connected to increase the water output. FIG. 6 schematically shows connecting solar water heaters into a series. Connector pipes (24) and (25) are used to connect two tanks together to increase capacity. The heaters are installed at the suitable angle, for example, on the roof of a dwelling. Water to be heated is fed through the inlet (11) and hot water is returned through the outlet (12) when needed. Water is heated by the sun illumination, assisted by convection flow in the tank. Water may in addition be heated using the electrical element. The heat of the water is retained with the aid of insulation materials. The glass sheet also traps heat, as mentioned, between glass and the tank surface. If the water gets too hot and too much pressure builds up inside the tank, the pressure-release valve releases pressure to a predetermined level. The braces facilitate use of the tank at a higher pressure than would be possible without them.

The solar water tank according to the invention is relatively inexpensive to manufacture, it requires minimal maintenance, and is easy to install. The tank is also easy to be employed in a modular form; two or more tank may be connected together to increase the overall capacity. All components of the tank are, in a preferred embodiment, made of recyclable materials. Solar water heaters are often constructed to be connected to the water pressure line, necessitating to include safe high pressure and sealed joining of the components, such as of the tank with pipes; the current heater may work without being connected to water grid. Existing heaters usually comprise two main parts and many internal components, and the assemble and installation requires trained experts. The current heater comprises one main part combining the tank and collector in one integral body made of a thermoplastic polymer. The heater introduces a unique design comprising two parts, preferably each exhibiting a mirror symmetry, apposed and connected, preferably by thermal welding. This enables a simple process of injecting one shape. Each part may be shaped so that the circumferential side wall includes rails for keeping insulating sheets, either of glass or plastic, reducing the heat losses from heated water, without requiring additional components to be added to the assembled heater. The outer wall may be roughened or otherwise structured, preferably during the injection process, to increase the heat absorption into the water, from the space between the glass pane and the parallel plastic wall.

Thus, in a preferred embodiment of the invention, provided is a solar water heater in which the tank and the collector are integrated in one compact parallelepiped unit made of polypropylene or other plastic. A glass pane is mounted on the outer surface oriented toward the sun, and a plastic slab is mounted on the opposite outer surface to form an insulation layer of the air.

The two internal surfaces are connected by many protrusions growing from them like stalagmite columns to improve rigidity of the flat heater unit. The cross section of the protrusions may be, for example, circular for cylindrical or cone-like protrusions. Said cross section, in a preferred embodiment, has a shape suitable for mass production with injection molding technology, and for maximally reinforcing final bodies of the heaters made by connecting two parts by hot welding. One such cross section is a shape of cross formed by two perpendicular ovals or rectangles. The heater unit has, in one embodiment, a collecting surface of about 1 to 2 m², a mass of about 20-40 kg and an internal free volume of about 80-150 liters. The parameters are, in one particular embodiment, 1.4 m², 25 kg, and 85 liter. The unit is manufactured by injection molding of identical half-units in the shape of open box with many stalagmite protruding perpendicularly from its internal surface, followed by heat-welding two identical parts placed as mirror images one onto the other. Inlets for tubing, holes for screws, manipulation handles and other shape elements are preferably formed during the injection molding of the half units. The solar heater may be connected to a water source, wherein the water pressure is less than 1.5 atmosphere. The source may include water line, or a water container positioned above the heater and supplying water by the force gravitation.

In another embodiment of the invention, the circumferential rip of the heater body and its base may be adjusted for holding the insulation material. Also included are the means for holding and lifting the product in the time of production, transport, and installation. The means for precise positioning of the two half-units before welding them together are a part of the process according to the invention. The columns reinforcing the whole structure of the heater may be 5-10 cm from each other, their diameter being from 1-4 cm of suitable cross section shape. The two parallel planes may be 8-12 cm distant. Each column is joined with its mate sticking from the opposite plane during the process of heat welding, like stalagmites and stalactites which unite in the limestone caves to form columns between the ceiling and the ground.

The target locations for introducing the heater according to the invention include the sun belt countries, but also other countries when hot water is needed for practical purposes without higher investments, including work sites outside cities, especially during summer, or recreation sites, for example, summer camps, etc. The heater of the invention, although ready for immediate use without special requirements even in the field conditions, can be, on the other hand, combined with additional means, enabling to assemble versatile systems for providing large volumes of hot water without excessive investments. The heater, in one embodiment, may be provided by auxiliary electrical heating, as well as pressure and temperature regulation means. The heater in an important aspect of the invention is a modular unit to be incorporated in a series of more units providing the required volume of water. The source of water for filling a heater or a heater series may be a container from which the water is either pumped or flows by gravitation. In village condition, water may be pumped, for example, from a well. Water may be brought from regular water line, if the pressure at the inlet to the first heater is not greater than 1.5 atmospheres, and in typical heaters not greater than 1 atmosphere. Pressure reducers may be incorporated between the source and the heater, when needed. The heater may work in batch-like mode, heating a certain amount of water for its complete use, either directly or after dilution with cold water. The heated water portion of, for example 85 liters having, for example, 80° C., may be suitable for washing clothes, whereas diluting with 170 liter cold water may provide about 250 liters of warm water for a shower. The heater may work in a continuous mode, when the heater is connected to a water source.

As mentioned, even new heater designs frequently keep the traditionally dual shape of a cylinder put on a slab, unable to get free of the barrel-like tank connected with a planar collector. The invention now provides a heater which integrates the collector and the tank in a single structural unit; furthermore, the heater of the invention employs no partition means for separating a) water which absorbs heat and increases its temperature from b) water stored for later use and losing heat. Simple and compact structure, economical to manufacture, and easy to install and operate, is now provided by this invention.

The invention will be further described and illustrated by the following example.

EXAMPLE

An injection molding machine, with 2800 ton clamping force was employed, to inject the 2 identical subunits. The 2 subunits were welded in a specially designed welding machine. The injected identical half-units had a mass of 15 kg each, the whole unit after welding had a collecting surface of 1.5 m², a mass of 30 kg and an internal free volume of about 120 liters. The upper face, the bottom face, and the lateral faces, structured similarly as in FIG. 3, were 10 mm thick. The injected body had a threaded inlet and outlet inside the lateral walls, 4 cm in diameter. Reinforcing columns were placed 10 cm from each other in a square network, having a shape of two 3 cm×1 cm perpendicular rectangles crossing each other in the middle. The two parallel outer walls were 10 cm distant after welding, the insulating spaces between the walls and the two insulating sheets were 3 cm wide on both sides. One insulating sheet was transparent to allow the sun radiation in. After filling with water and exposing to the sun light, water reached 60° C. and 80° C. when measured in the inlet and outlet positions, respectively, exposed for 9 hours when positioned at the angle of 45°.

While the invention has been described using some specific examples, many modifications and variations are possible. It is therefore understood that the invention is not intended to be limited in any way, other than by the scope of the appended claims. 

1. A solar water heater comprising a container for holding water of a volume between 60 and 200 liter, and a sun light collector of a surface between 0.8 and 2 m², integrated in one body essentially having a parallelepiped shape, the body comprising two connected half-units, each unit injection molded from a thermoplastic polymer, and each unit provided with a plurality of columns protruding through the internal volume of said heater, wherein each column touches a column from the other half-unit without compartmentalizing said inner volume.
 2. A solar water heater according to claim 1, said two half-units being heat welded or bonded.
 3. A solar water heater according to claim 1, said two half-units being identical or different.
 4. A solar water heater according to claim 1, essentially having the shape of a flat parallelepiped made of two plastic, injection molded, half-units, comprising rectangular upper and bottom faces, and a transparent sheet mounted on said upper face and a non-transparent sheet or insulating layer mounted on or in said bottom face.
 5. A solar water heater according to claim 1, wherein said body comprises an upper face and a bottom face of the same rectangular shape, and columns protruding from said upper face downward and columns of the same shape protruding from the bottom face upwards, the two column systems being positioned against each other, each column touching a column from the opposite wall, the double column height essentially determining the distance of said two faces, each pair of the opposite columns being tightly connected by heat welding or by bonding.
 6. A solar water heater according to claim 1, comprising no partition means for separating water absorbing the sun light from water stored for later use.
 7. A solar water heater according to claim 1, consisting essentially of three main structural components: one compact body, a transparent sheet, and a non-transparent sheet, the heater being made of plastic, except for said transparent sheet which may be made of glass.
 8. A solar water heater according to claim 7, wherein said compact body has an upper face and a bottom face and is obtained by heat welding or by bonding of two identical half-units prefabricated by injection molding, said transparent sheet mounted onto said upper face and said non-transparent sheet onto said bottom face.
 9. A method for manufacturing a solar water heater having a container for holding water and a sun light collector of a rectangular surface integrated in one body essentially exhibiting a parallelepiped shape, comprising i) injection molding a half-unit having essentially the shape of a an open flat parallelepiped having one base and lateral faces, the base and faces defining a half of the internal volume of said heater, and columns protruding from said base within the internal volume having a height approximately equal to the height of said faces; ii) precisely apposing two half-units molded according to step i) in such a way that each column from one half-unit touches a columns from the second half-unit; iii) joining said two half-units, without compartmentalizing the inner volume of the heater, thereby closing said internal volume in a water-proof manner, the volume serving as a tank for containing water to be heated; and iv) mounting a transparent sheet onto one base of said tank, and a non-transparent sheet onto the other base of said tank.
 10. A method according to claim 9, wherein said two half-units are joined by heat welding or by bonding.
 11. A method according to claim 9, wherein said two half-units are identical.
 12. A method according to claim 9, wherein said heater comprises a plastic body formed by welding two identical half-units each formed by injection molding, said body having an upper face, a bottom face, and lateral faces, said upper face being depressed and said bottom face being elevated, said upper face enclosing an upper insulating air layer together with the lateral faces and said transparent sheet, and said bottom face enclosing a layer of insulating materials together with the lateral faces and said non-transparent sheet.
 13. A method according to claim 9, wherein said injection molded half-units comprise structural features enabling to functionally close the internal volume of the water tank, to mount the transparent and non-transparent sheets on the tank, and to connect the heater with pipes and desired accessories.
 14. A method according to claim 9, wherein said injection molded half-units are shaped to provide maximal mechanical strength at minimal weight.
 15. A method according to claim 9, wherein the main structural component of said sun water heater consists merely of one compact polymer body, obtained by bonding or by heat welding of two identical half-units prefabricated by injection molding of a thermoplastic polymer. 